Mechanical warewashing machines have been common in institutional and household environments through the years. Such mechanical automatic warewashing machines are designed to operate with two or more cycles which include initially a wash cycle followed by a rinse cycle. Such dishwashers can also utilize a soak cycle, a prewash cycle, a main wash cycle, a rinse cycle, a sanitizing cycle and a drying cycle if required. Such cycles can be repeated and additionally cycles such as a scraping cycle, i.e., a rinse cycle before a wash cycle can be used, etc. After passing through a wash cycle, flatware, dishware, kitchen ware, cups, glasses, knives, forks, spoons, etc. can exhibit spotting that arises from the uneven draining of the water from the surface of the ware after the rinse step. Spotting is aesthetically unacceptable in most consumer and institutional environments.
In order to substantially prevent the formation of such spotting, rinse agents have been commonly added to an aqueous diluent to form an aqueous rinse used in a rinse cycle. The precise mechanism through which rinse agents work is not well established. One theory holds that the surfactant in the rinse aid is absorbed on the surface at temperatures at or above its cloud point, and thereby reduces the solid-liquid interfacial energy and contact angle. This leads to the formation of a continuous sheet which drains evenly from the surface and minimizes the formation of spots. Generally, high foaming surfactants have cloud points above the temperature of the rinse water, and, according to this theory, would not promote sheet formation, thereby resulting in spots. Moreover, high foaming materials are known to interfere with the operation of the warewashing machine.
Rinse additives are well known to the trade and have been in use for thirty or more years. However, there is an unmet need for rinse additives which are made entirely of food additive materials; this is a very challenging situation since it greatly limits what can be used in the formulation; it is also a very unique situation in that few combinations will work that meet the food additive criteria. Common rinse additive formulas are used in amounts of less than about 1000 parts of the rinse aid or active sheeting agent per million parts of the aqueous rinse. Rinse aids available in the consumer and institutional markets comprise liquid, thickened semi-liquid or solid forms which are typically added to or dispersed or dissolved in aqueous diluents to form an aqueous rinse prior to use. Such dissolution or dilution can occur from a rinse agent installed onto the dish rack or can be dispensed from a dispenser integral with the machine or from a separate dispenser that is cooperatively mounted near or onto the exterior of the dish machine. Many commonly available active ingredients for rinse agents are made of polyalkylene oxide substituted materials preferably ethylene oxides/propylene oxide block copolymers.
A substantial need has arisen to obtain rinse compositions comprised solely of food additive ingredients. We have discovered that a class of nonionic surfactants, namely, the polyalkylene oxide derivatives of sorbitan fatty acid esters have surprising levels of sheeting action and can be formulated into effective rinse agents with a careful selection of defoamer compositions. We have found that these nonionic sorbitan based surfactants can be effectively defoamed with materials approved as food additives. We have found that these defoamers are compatible with sorbitan materials in the rinse agents and the agents can be combined with an aqueous diluent to form an effective aqueous rinse. The rinse agent of the invention is preferably a liquid that can be metered or diluted into an aqueous rinse stream in controlled proportions.
Haslop et al., U.S. Pat. No. 4,618,446, teaches a variety of ingredients for use in spherical liquid detergent compositions.
Haslop et al., U.S. Pat. No. 4,793,943, teaches a variety of ingredients useful for making liquid detergent compositions.
Akred et al., U.S. Pat. No. 4,871,467, teaches a variety of compositions and materials used to form non sedimenting liquid detergent compositions.
Aronson et al., U.S. Pat. No. 5,045,225, teaches a combination of hydrocarbon oils and silicone compositions as antifoam materials.
Gentle et al., U.S. Pat. No. 5,073,298, teaches silicone silicate based defoaming compositions.
Chun et al., U.S. Pat. No. 5,133,892, teaches machine dishwashing detergent tablets having timed release of enzyme and chlorine bleach and a variety of other ingredients used in making the detergent composition.
Tsukada, Japanese Patent Application Publication Kokai 49-126,703, teaches carbohydrate aliphatic ester rinse agents.
Miura et al., Japanese Patent Application Publication Kokai 50-62,211, teaches polyhydric alcohol containing rinse agents.
Miura et al., Japanese Patent Application Publication Kokai 51-68,608, teaches polyol aliphatic ester containing rinse agent compositions. Suzuki et al., Japanese Patent Application No. 86-31,272, teaches a rinse agent comprising a polyethoxylated sorbitan fatty acid ester glycerol and a sugar alcohol.
Suzuki et al., Japanese Patent Application No. 86-161,193, teaches a similar material.
Nantaku, Japanese Patent Application No. 59-187,096, teaches a polyglycerine ester of a C.sub.6-8 fatty acid containing rinse agent.
Wilson et al., "Rinse Additives for Machine Dishwashing", Soap and Chemical Specialties, pp 48 et seq. (February 1958), discussed the basic technology regarding rinse agent formulation.
None of the prior art recognize the sheeting action of the nonionics of the invention nor combine the preferred high cloud point, high foaming surfactants with appropriate defoamers to achieve a rinse agent that can be diluted into an aqueous rinse providing low foaming sheeting properties.